The present invention relates to a matching circuit and a plasma processing apparatus used for manufacturing electronic devices of semiconductors, liquid crystal devices and so on and micro machines.
In manufacturing electronic devices of semiconductors, liquid crystal devices and so on and micro machines, a thin film processing technology by plasma processing has been used. FIG. 4 shows a typical plasma processing apparatus. A gas supply system 2 is provided on the sidewall of a vacuum vessel 1. Air discharging is performed by a turbo-molecular pump 4 through an exhaust port 3 provided on a bottom wall while a prescribed gas is supplied to the inside by the gas supply system 2, and the vacuum vessel 1 is internally kept at a prescribed pressure. A pressure regulating valve 5 for controlling the inside of the vacuum vessel 1 to a prescribed pressure is provided above the exhaust port 3 so as to move up and down. A substrate electrode 7, on which a substrate 6 to be subjected to plasma processing is placed, is fixed via four props 8 inside the vacuum vessel 1. The substrate electrode 7 is supplied with a high-frequency power of a frequency of 500 kHz from a high frequency power source 9 for the substrate electrode. An inner chamber 10 is provided particularly around the substrate electrode 7 inside the vacuum vessel 1, so that the inner wall surface of the vacuum vessel 1 is prevented from becoming dirty due to the plasma processing.
Moreover, a disk-shaped antenna 11 is fixed on the inner surface of the upper wall of the vacuum vessel 1 via a dielectric plate 12 oppositely to the substrate electrode 7. The lower surface of the antenna 11 is covered with a cover 13. Around the antenna 11, a conductor ring 14 is fixed via a dielectric ring 15 on the inner surface of the upper wall of the vacuum vessel 1. With this arrangement, an annular plasma trap 16 is provided between the conductor ring 14 and the antenna 11 and between the dielectric ring 15 and the dielectric plate 12. The antenna 11 is provided with a feeder rod 17 that penetrates through the dielectric plate 12 and the upper wall of the vacuum vessel 1, and the feeder rod 17 is supplied with a high-frequency power of a frequency f=100 MHz from a high-frequency power source 18 for the antenna via a matching circuit 20 by way of a coaxial pipe 19.
If the substrate electrode 7 and the antenna 11 are supplied with the high-frequency power in a state that the vacuum vessel 1 is internally discharged and filled with a prescribed gas at a prescribed pressure, then plasma is generated in the vacuum vessel 1, causing the substrate 6 placed on the substrate electrode 7 to be subjected to plasma processing.
The matching circuit 20 is to reduce the power loss by matching the impedance of the antenna 11 with the characteristic impedance of the coaxial pipe 19 that serves as a coaxial line. The matching circuit 20 is constructed of the circuit shown in FIG. 5. That is, to an input terminal 21 to which the coaxial pipe 19 is connected, one terminal of a first variable capacitor 22 that serves as a first variable reactance element is connected via a copper plate 23 that acts as inductance. The other terminal of the first variable capacitor 22 is grounded via a casing 24. One terminal of a second variable capacitor 25 that serves as a second variable reactance element is connected to the input terminal 21 via a copper plate 26 that acts as inductance. The other terminal of the second variable capacitor 25 is connected to an output terminal 27 of the matching circuit 20 to which the antenna 11 is connected.
However, the matching circuit 20 of the conventional plasma processing apparatus has had a narrow range in which matching can be achieved. Thus, the matching circuit 20 has been able to secure the matching only on limited discharge conditions even when the discharge conditions of the type and flow rate of gas, the pressure in the vacuum vessel, the high-frequency power and so on have been changed. Moreover, if any of the gas type, the gas flow rate, the pressure in the vacuum vessel and the high-frequency power is changed during the plasma processing, then it sometimes takes about five to ten seconds to the attainment of a matched state when the change in the impedance of the antenna 11 before and after the change is large. If the change in the impedance of the antenna 11 is too large, the matched state has sometimes been unable to be secured. Furthermore, if the frequency of the high-frequency power applied to the antenna 11 is increased, then an excessive current flows through the first variable reactance element 22 and the second variable reactance element 25 of the matching circuit 20, and an overvoltage is generated across the terminals particularly of the second variable reactance element 25. This has consequently led to a problem that the temperature has locally risen and the matching state has become unstable.
The present invention has been accomplished in view of the aforementioned problems and has the object of providing a matching circuit and a plasma processing apparatus, which have a wide range in which matching can be achieved and the matched state of which is stable with respect to a change in the load state.
As a means for solving the aforementioned problems, the present invention provides a matching circuit comprising:
an input terminal;
an output terminal;
a first fixed reactance element;
a second fixed reactance element connected in series to the first fixed reactance element the other terminal of which is grounded;
a first variable reactance element one terminal of which is connected to the input terminal and the other terminal of which is connected to a point between the first fixed reactance element and the second fixed reactance element;
a second variable reactance element one terminal of which is connected to the second fixed reactance element and the other terminal of which is grounded; and
a stripline one terminal of which is connected both to the second variable reactance element and the second fixed reactance element and the other terminal of which is connected to the output terminal.
Assuming that a high-frequency power applied to the input terminal has a wavelength of xcex (m), then a sum total D1+D2 of a length D1 (m) from the output terminal to an antenna connected to the output terminal and a length D2 (m) of the stripline should preferably satisfy the expression of:
xcex/32+xcex/2xc3x97(nxe2x88x921)xe2x89xa6D1+D2xe2x89xa6xe2x88x92xcex/32+xcex/2xc3x97n (n=1, 2, 3, . . . ) 
It is more preferable that the length D1+D2 satisfies the expression of:
xcex/16xe2x89xa6D1+D2xe2x89xa64xcex/16. 
The first variable reactance element and the second variable reactance element can each be a variable capacitor. It is preferable that each of the first fixed reactance element and the second fixed reactance element is a coil and the elements are connected in series to constitute one fixed coil. The first fixed reactance element and the second fixed reactance element can each be replaced by a variable reactance element.
As a means for solving the aforementioned problems, the present invention provides a plasma processing apparatus including a vacuum vessel; a gas supply system for supplying a gas into the vacuum vessel; an exhaust system for evacuating the inside of the vacuum vessel; a substrate electrode, which is provided inside the vacuum vessel and on which a substrate to be processed is placed; a substrate electrode high-frequency power source for supplying a high-frequency power to the substrate electrode; an antenna arranged oppositely to the substrate electrode; an antenna high-frequency power source for supplying a high-frequency power to the antenna; and a matching circuit arranged between the antenna and the antenna high-frequency power source, the matching circuit comprising:
an input terminal;
an output terminal;
a first fixed reactance element;
a second fixed reactance element connected in series to the first fixed reactance element the other terminal of which is grounded;
a first variable reactance element one terminal of which is connected to the input terminal and the other terminal of which is connected to a point between the first fixed reactance element and the second fixed reactance element;
a second variable reactance element one terminal of which is connected to the second fixed reactance element and the other terminal of which is grounded; and
a stripline one terminal of which is connected both to the second variable reactance element and the second fixed reactance element and the other terminal of which is connected to the output terminal.